Gotta question. 94 firebird transmission keeps going out. Has been changed 2  times. First time, Car would move but would not shift to well. Kinda jerky in the shifts, and setting at a light it would sorta go into and out of gear. Pull it into first and it would go and then it would shift.

That's a 4L60E, electronic unit(the electronic equivalent of the 700R4).
Salvage yard finds are a crap shoot, at best. I'd venture a guess that the two you got were not good ones, regardless of what you were told.
The first one sounds like it may have just been burnt up. The second one could simply be a bad shift solenoid, or even the speed sensor on the tailhousing, if it came with the trans.

What was the original reason for replacing the trans to start with?

torque converter was bad. Or so I was told. I had traded a 65 tbird for it.

If the TC failed, it most likely shelled out a lot of metal, which then circulated all thru the trans, and the trans cooler, located in the radiator. IF the cooler was not flushed out properly(if at all), the remaining metal will continue to be flushed out with the new trans fluid, into the "new" trans. That can cause all kinds of problems with valves, and wear on the bushings, as well as major wear in the pump.
If she decides to have the trans rebuilt somewhere, they need to bypass the radiator cooler completely, and install an auxiliary trans cooler.

sounds right. Thanks!